Accurate laboratory rest frequencies of vibrationally excited CO up to $varv = 3$ and up to 2 THz

TL;DR

This paper reports highly accurate laboratory measurements of vibrationally excited CO's rotational frequencies up to 2 THz, enabling precise astronomical observations of high-temperature regions in space.

Contribution

The study provides the first high-precision laboratory frequency data for vibrationally excited CO up to $ u=3$ up to 2 THz, improving spectral predictions for astrophysical research.

Findings

Measured CO rotational spectra between 220 and 1940 GHz.

Determined rotational constants and distortion parameters with high accuracy.

Predicted accurate rest frequencies of vibrationally excited CO beyond 2 THz.

Abstract

Astronomical observations of (sub)millimeter wavelength pure rotational emission lines of the second most abundant molecule in the Universe, CO, hold the promise of probing regions of high temperature and density in the innermost parts of circumstellar envelopes. The rotational spectrum of vibrationally excited CO up to $\varv = 3$ has been measured in the laboratory between 220 and 1940 GHz with relative accuracies up to $5.2 \times 10^{-9}$, corresponding to $\sim 5$ kHz near 1 THz. The rotational constant $B$ and the quartic distortion parameter $D$ have been determined with high accuracy and even the sextic distortion term $H$ was determined quite well for $\varv = 1$ while reasonable estimates of $H$ were obtained for $\varv = 2$ and 3. The present data set allows for the prediction of accurate rest frequencies of vibrationally excited CO well beyond 2 THz.